The prevalence of root-surface caries is positively correlated with age, number of teeth and gingival recession. A simultaneous increase in the mean age of the American population, and decreases in edentulousness in all age groups and coronal caries in children suggests that treatment needs for root caries in older individuals may increase. The long-term objective of this proposal is a model in which preventive measures to reduce the incidence of root-surface caries following alveolar bone loss can be tested in a conventional laboratory rat. The specific aims of the proposed project are to determine the effects of selective gingivectomy on alveolar bone loss in Sprague-Dawley derived rats; to determine the effects on root surface caries following gingivectomy of inoculation with microorganisms associated with root surface caries in humans; to determine the effect of sucrose in the diet on root surface caries following gingivectomy. Two experiments are proposed. In the first, four groups of Sprague-Dawley rats will have their oral flora depressed with antibiotics. One group will be maintained "clean", the other three groups will be "conventionalized" and infected orally with 1. S. mutants 6715, or 2. A. viscosus M-100 or 3. both. All four groups will be maintained on diet MIT 200 (67% sucrose). At 30 days of age all the animals will receive a gingivectomy in a mandibular and contralateral maxillary quadrant. The rats will be sacrificed 60 days post-operatively. The extent of alveolar bone loss and carious root surface involvement will be measured planimetrically via a computer based image analysis system. To test the effect of the sucrose content of the diet on root surface caries following alveolar bone loss and on the virulence of the cariogenic microorganisms, a second experiment is proposed. Five groups of Sprague-Dawley rats will have their oral flora depressed with antibiotics. At weaning the groups will be conventionalized and inoculated with S. mutans and A. viscosus except as noted. Group I will be fed diet MIT 200, group II diet MIT 305 (5% sucrose), group III diet MIT 300 (0% sucrose), group IV will be fed MIT 305 and inoculated with S. mutans 6715, group V will be fed diet MIT 305 and inoculated with A. viscosus. The animals receive gingivectomies at 30 days. The rats will be sacrificed 60 days postoperatively and evaluated for alveolar bone loss and root surface caries.